Chase's website was slow and unavailable for some users for several hours on Wednesday, one day after Bank of America experienced similar issues.
Around 1:40 p.m. ET on Wednesday, Chase's Twitter account tweeted: "Chase.com is experiencing intermittent issues. We're working to restore full connectivity & apologize for any inconvenience." Chase spokesman Patrick Linehan repeated a similar statement, and declined to comment further on the reason for the problems.
Monitoring firm Keynote says the trouble appeared to start around 12:15 pm ET and was mostly resolved by the late afternoon, although some sluggishness remained.
Chase's site issues broke out just as Bank of America(BAC) was recovering from its own intermittent slowness. Bank of America didn't reveal the cause of its glitches, but both banks recently rolled out changes to their website that could have inadvertently caused a problem.
On blogs and Twitter, some hacker groups were claiming responsibility for the issues at both banks. The problems at both banks began soon after one group posted messages on Pastebin calling for attacks on the banks' sites. The website of the New York Stock Exchange, also mentioned as a target in Tuesday's message, did not suffer any apparent outages.
The favorite weapon for these kinds of cyberattacks is a "distributed denial of service" (DDoS) attack, which directs a flood of traffic to a website and temporarily crashes it by overwhelming its servers. It doesn't actually involve any hacking or security breaches. A DDoS attack would typically cause the type of slowness and intermittent unavailability that both Chase(JPM) and Bank of America experienced this week.
But there was no immediate evidence to support the hackers' claims, and several recent ones turned out to be hoaxes. Earlier this month, a person affiliated with the hacktivist collective Anonymous said the group took down the web hosting service GoDaddy, and in June the group UGNazi claimed responsibility for downing Twitter. Both outages were later revealed to be technical issues.
"I can assure you we continuously take proactive measures to secure our systems," Bank of America's spokesman said on Tuesday in response to a question about whether the company had seen any signs of a cyberattack. Chase's spokesman declined to comment about the issue.